Antarctic glacier moves with a fast slip like an earthquake, but at a glacial pace.

Tony Fitzpatrick from Washington University in St. Louis reported on new research into glacial movement in Antarctica. Seismological combined with GPS analysis has led a group of scientists to a new understanding of how glaciers move in Antarctica.

Douglas A. Wiens, Ph.D., professor of earth and planetary sciences in Arts & Sciences, a seismologist at Washington University in St. Louis along with colleagues at Pennsylvania State University and Newcastle University in the United Kingdom analysis revealed two bursts of seismic waves from an ice stream in Antarctica every day, each one equivalent to a magnitude seven earthquake.

“Glaciologists had thought that they understood how glaciers move, and they thought the ice moves move slowly and continuously by creep, but now this indicates that they move with a fast slip, almost like an earthquake,” Wiens said.

The ice stream is a giant glacier 60 miles wide and one-half mile thick. The data show that the river of ice moves about 18 inches within ten minutes, remains still for 12 hours, then moves another eighteen inches. Each time it moves, it gives off seismic waves that are recorded at seismographs all around Antarctica, and even as far away as Australia. Prior to this discovery, researchers were not aware that ice streams radiated seismic waves. Dr Weins described the phenomena:

“By some measures, the seismic impact is equivalent to a very large earthquake, but it doesn’t feel like it because the movement is much slower than a real earthquake. The data look an awful lot like an earthquake, but the slip lasts for 10 minutes, while on the other hand an earthquake of this size would last for just ten seconds. I guess you could call it an earthquake at glacial speed. This is very strange behavior, and we need to understand more about it.”

“The GPS shows us directly how the ice stream moves. The slip starts in a certain part of the ice stream and then it moves out, rather like a landslide might start at a certain point and then move out to envelop an entire mountainside. The GPS tells us which part moved first and what other parts moved next and so forth.”

The data show that the slip always starts from the same spot on the bed of the ice stream — what glaciologists call a “sticky” spot — which has more friction than the surrounding part of the bed.

Dr Wiens said that it is important to understand the physics behind what is controlling this kind of slip.

“This stick-slip phenomenon may provide a clue about what makes these ice streams move faster or slower,” Wiens said. “This particular ice stream has been slowing down over the last few decades, and no one knows why. “

The study was published in the June 5 issue of Nature Online and was funded by the National Science Foundation.


The Canada Glacier extends into the Taylor Valley toward Lake Hoare.

Canada Glacier.

Photograph by: Emily Stone, National Science Foundation. Date Taken: January 16, 2006

~ by abstraktbiblos on Thursday, 5 June, 2008.

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